Did you check your Power Management settings in your BIOS? It sounds like you have a system problem.
The usual causes for random shutdowns are:
1)Overheating triggers auto-shutdown to protect the CPU. Your reported temp is good, but for HD. What is the Processor temp?.
2) Memory module going bad. Bad memory stick causing propblems, especially during gaming when usage is high.
3) Power supply going bad. A good possibility on a clone, especially if you installed new cards for gaming which may be drawing more power than PS can handle.
4) Using something like Intel's gaming console where you can set a lot of parameters, the shut down temp may not be set correctly (toolow).
5) Possibly a virus may be causing your shut down problem. I've seen some malware that does this. If it is malware/trojan it will initiate the 30 second shutdown upon detection. Need to see and read instructions
in the Malware Removal section of this form.
Probably left out something.
Hope this helps.